This invention relates to systems for containing and dispensing fluids and is particularly concerned with systems for containing, transporting, and dispensing hydraulic fluids and engine oils for jet airplanes.
Hydraulic fluids find numerous commercial uses, an especially common application being in the aircraft industry, where they are employed in the systems that operate the rudder, wing flaps, landing gear, etc. It is extremely important that these fluids be protected from dirt and water, both of which can cause serious damage to the hydraulic systems of aircraft. Hydraulic fluids are also extremely corrosive and are especially damaging to painted surfaces, and great care must be exercised to avoid spillage, both in filing the containers and in servicing the aircraft. Synthetic engine oils are hygroscopic and especially susceptible to contamination with water, which reacts with phosphate esters in the oil to produce a highly corrosive acid that etches the metal of the engine and causes serious damage. The deleterious effect of dirt in lubricating oil is even more pronounced than in hydraulic fluid.
In servicing aircraft, a container of fluid (i.e., hydraulic fluid or engine oil) is moved to the aircraft, hoses extending from the container connected to the appropriate system on the aircraft, and the fluid pumped into the system. For many years it has been common to use containers that are 5-gallon tanks made of corrosion-resistant stainless steel incorporated in a two-wheeled cart to facilitate moving to and from the aircraft to be serviced. To fill this tank, a large fill cap on the top is opened, exposing the interior of the container to the atmosphere, which is inevitably contaminated with moisture and dust particles. In humid weather, moisture condenses on the metal tank, inevitably resulting in the presence of water in the contents. Further, the useful life of the tanks is on the order of two years, after which they develop stress cracks, through which the fluid seeps. These cracks cannot be successfully repaired by welding, so the tank must be disposed of, a process more expensive than might be realized. Environmental regulations require that the tanks be cut in half and solvents used to leach out the oil clinging to the interior surfaces. rior surfaces. Disposal of the fluid-containing solvent then presents a still further expensive problem. Additionally, because the stainless steel tank and the cart form an integral unit, the entire unit is effectively destroyed when the tank must be replaced.
At least one airline in recent years has replaced the stainless steel pump cart with a flat-topped crosslinked polyethylene tank removably mounted on a two-wheeled wire-formed cart to which it is attached by bolting an angle plate to the rear portion of the top. A hand pump, vent fitting, and a self-sealing quick disconnect fill fitting extend through the plate into the tank. The angle plate is then attached to a flat plate on the back of the cart, so that a damaged tank can easily be removed and replaced. The quick disconnect fill fitting provides for clean, uncontaminated entry of fluid into the tank. A coalescent filter is mounted on the vent to dry the air that enters the container as the fluid is pumped out. A filter is also inserted in the dispensing line to block any particulate matter that may be entrained in the fluid. A spring-loaded check valve is inserted in the air vent line to prevent the entry of fluid if the cart is overturned. Moisture does not condense in or on the polyethylene tank in the same way it does on a stainless steel tank.
Although the containing and dispensing system just described offers a significant improvement over its stainless steel predecessor, it is not without its own problems. For example, a gasket seal is provided between the angle plate and the flat top of the tank, permitting the seepage of fluid laterally through the gasket, especially as it shrinks and disintegrates with age, and occasionally allowing the entry of moisture and particulate matter that is inevitably present on the flat top of the tank. To some extent, the same problem exists with respect to the quick disconnect fill fitting. The lower front edge of the polyethylene container is subjected to abrasive wear as the cart is moved from place to place. The drying filter for the vent does not completely block the entry of particulate matter. The crosslinked polyethylene tank can not be recycled. The wire-formed cart is susceptible to twisting and distortion. The steel wheel bearings on the cart tend to be adversely affected by cold weather, and the aluminum wheels themselves are attacked by exposure to the environment and water-contaminated engine oil. If the cart is inadvertently overturned, there is highly undesirable oil leakage from the line through which venting air is supplied, the dual spring-loaded check valve arrangement in the line being unable to prevent this problem.
The present invention is directed to improving the polyethylene tank and cart to overcome the problems just discussed.